Rig tuning and set up

Dart Sails’s guide to Rig setup

This is a very general guide to setting a Hunter Impala 28 rig written by Sean Semmens from Dart Sails.

Dart Sails can provide a championship winning sails complete with a detailed tuning guide to alter the rigging to suit various conditions. Designed by Sean Semmens multiple class champion. After many years as Sail designer at Westaway Sails, Sean is continuing to develop Impala sails combining new materials with historic knowledge of successful sail shapes.

The object of this guide is to offer an initial starting point, which will offer competitive mast set up for various different sail manufacturers.

Conditions True Wind Strength Rigging Tension

New Loos Gauge

Caps / Lowers

Rigging Tension

Old Loos Gauge

Caps / Lowers

Rigging adjustments

½ turns from Base

Survival Above 25 knots 39 / 32 42 / 35 Caps + 13, Lowers No.3 or 4
Heavy 18 – 25 knots 38 / 31.5 41 / 36 Caps = 10, Lowers + 13 No.1 or 2
Medium (Base) 10 – 28 knots 33 / 17 36 / 25 Base No.1
Light 5 – 10 knots 25 / 10 31 / 15 Caps – 6, Lowers – 3 No.1
Drift Less than 5 knots 20 / slack 24 / slack Caps – 9, Lowers – 6 No.1

First you will need to ensure that the mast is completely upright (sideways) in the boat. You will need to tension all four shrouds hand tight. Attach a long steel tape measure to the main halyard and hoist to the top of the mast. Measure down to the aft quarters of the deck (the top of the deck port and starboard as far aft and outboard as possible). Tension the cap shroud on the side of the yacht that gave the largest reading. It is wise to only adjust 2 turns on the rigging screw at a time, then tension the lower shroud to keep the spar in column sideways. Re-measure and repeat the exercise until the mast is upright and in column sideways.

Most Impalas use 6mm 1×19 or 6mm dyform shrouds. Smaller 5mm shrouds are allowed in the class rules but stretch in stronger winds. For the purpose of rig tensions we have assumed that your Impala has 6mm dyform shrouds. You can purchase a rig tension gauge which will enable you to repeat shroud tensions. The most common gauge is a ‘Loos’ gauge. The original ‘Loos’ gauge is named Model B, this model gives similar but not identical readings to a meter supplied by the spar makers ISP better known as Superspars. In the last year or so a more accurate meter called the ‘Loos professional tension gauge’ (Model PT-2M) has been put onto the market and this is the model we recommend.

As a starting point we suggest that you tension the shrouds so that both the cap and lower shrouds read 33 on the ‘Loos’ gauge. This is very much a guide starting point which shroud be competitive in around 15 knots of wind.

As a guide cap shroud tension affects the tension in the forestay and as a result it affects the yachts pointing ability. A tight forestay allows a flat entry to the genoa and therefore high pointing and less power. A sagging forestay reduces pointing but increases power. In stronger winds (15 knots and above) pointing upwind is very important as the yacht has already reached near maximum boat speed. In very strong winds you may feel the need to increase the cap shroud tension to around 39. In lighter winds pointing the boat upwind is not as important as boat speed so we recommend easing the cap shroud tension to around 25 or even less in very light winds..

Lower shroud tension affects primarily the fore and aft bend in the mast. If with the mainsheet on, and the backstay eased, the mainsail has creases running from the clew to the luff up to about half way up the mast, then the mast is too bent and you should increase the lower shroud tension. Keep increasing this tension until the creases only reappear when the backstay is pulled on to maximum. If the mainsail is excessively full even when the backstay is on hard then the lower shrouds are too tight and should be eased. The tensions for the lower shrouds will vary for mainsail to mainsail. In light airs it is quite possible to need the mast totally straight (fore and aft) with the lower shrouds very slack to avoid the mainsail being too full. For medium wind strengths we suggest a mast bend with no backstay of 1 inch and for stronger winds maybe more depending on the shape of the mainsail.

When adjusting the rigging on the water either lower sails to adjust, or only adjust the leeward shrouds when sailing upwind then tack to adjust the other side. Attempting to adjust with shrouds under load may result in stripping the threads on the rigging screws and risks mast failure.

In general the mast rake (ie the angle off the vertical) can affect the upwind and downwind feel and performance of the yacht. Raked well aft the mast will improve upwind performance, hinder downwind performance and increase weather helm. A more upright mast will reduce weather helm or may even incur lee helm, improve downwind but hinder upwind performance. Never have a mast with a completely upright or forward raked mast.

Prior to measuring the rake the mast should be set up with a base/medium tensions, with 1 inch of pre-bend for and aft in the mast, with no mainsheet, vang, halyards tension or backstay.

To measure the rake take the Genoa halyard and close the snap shackle if it has on. Lay the halyard down the mast and tension the halyard so the bearing point of the snap shackle or end of rope is exactly in line with the top of the black band by the gooseneck. Make sure the halyard is cleated, then arc the halyard forward and mark the forestay where the same point on the halyard lies under the same tension. Then measure down from the point on the forestay to where the forestay intersects the deck at the bomb doors.

The regular rake setting should be 1.8m. If you are expecting to sail is light winds the rake can be reduced and have the mast more upright, removing a toggle is the best way to achieve an easy to change rig set up. A light airs set up would have a rake measurement of 1.75m taken as described above.

An alternative way to measure for the regular set up you should have a measurement of 12.225m from the top of the mast to the very aft quarters of the deck (top of the deck port and starboard as far aft as possible) and 11.40m from the top of the mast to the deck adjacent to the base of the shrouds.

To measure this you will need a calm day and a long steel tape measure. Do not forget to add the length of the snap shackle and knot or splice on the main halyard, so the distance measured is from the reference point to the main halyard sheave.

Sails to Sean’s designs have won the IRC National championships and the Impala National championships on many occasions over the past 20 years.

A more detailed rigging tensions guide for varying conditions to be used in conjunction with Dart Sails is available upon ordering new sails.

Contact Sean Semmens on 01803 839196 or 07717 500726

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